1. Field of the Invention
The present invention relates to apparatus and methods for controlling a plurality of electrical devices, and more particularly, to automatically configuring a series of electrical devices to either a local control mode or a remote control mode.
2. Description of the Related Art
It is often desirable to have the operation of one electrical device dependent on the operation of a different electrical device. For example, in a personal computer system, many electrical devices (for example, a main processing unit, a display and a printer) are interconnected and cooperate to form the system. It is both more convenient and more efficient to control the operational state of each electrical device at a single location.
One conventional configuration for controlling a plurality of electrical devices is shown, for example, in FIG. 1. A series of electrical devices 10.sub.1, 10.sub.2 and 10.sub.3 are connected via connecting cables 11 to pin connectors 12 on each of the electrical devices 10.sub.1, 10.sub.2 and 10.sub.3. A sense circuit 14.sub.1, 14.sub.2 and 14.sub.3 is provided in each electrical device for detecting a predetermined voltage condition on lines L.sub.1 and L.sub.2 of the cable. Actuation switch 15 is connected across the lines L.sub.1 and L.sub.2 of the cable. As shown, actuation switch 15 comprises a manual switch disposed remote from any of the electrical devices 10.sub.1, 10.sub.2 and 10.sub.3. Alternatively, actuation switch 15 may comprise a manual switch disposed on one of the electrical devices 10.sub.1, 10.sub.2 or 10.sub.3. Since sense circuits 14.sub.1, 14.sub.2 and 14.sub.3 are electrically connected in parallel between lines L.sub.1 and L.sub.2, each sense circuit 14.sub.1, 14.sub.2 and 14.sub.3 is responsive to actuation switch 15.
Switching circuitry 16.sub.1, 16.sub.2 and 16.sub.3 is provided in each of electrical devices 10.sub.1, 10.sub.2 and 10.sub.3 for switching the corresponding electrical device from a standby mode to an operational mode when a.c. power is provided to the corresponding electrical device. For purposes of this description, a.c. power is input to an electrical device and made available to switching circuitry to provide power to the electrical device when its external power switch 17.sub.1, 17.sub.2 or 17.sub.3 is turned ON. An operational mode is a mode in which a.c. power is provided to the electrical device and the electrical device is enabled to perform one of its intended functions. A standby mode is a mode in which a.c. power is provided to the electrical device, but the electrical device is not enabled to perform one of its intended functions.
An external configuration switch 18.sub.1, 18.sub.2 and 18.sub.3 is provided on each of electrical devices 10.sub.1, 10.sub.2 and 10.sub.3 for selecting whether the electrical device is to operate in a local mode or a remote mode, or is to be turned OFF.
In a local mode, an electrical device is not responsive to input signals from external sources, and the operational state of the electrical device is selected locally, i.e at that electrical device itself. An electrical device is configured to operate in a local control mode, as shown by electrical device 10.sub.1, by setting the configuration switch 18.sub.1 to a "local" position. This effectively prevents sensing circuit 14.sub.1 from sensing a voltage on lines L.sub.1 and L.sub.2. Instead, in response to the "local" selection of configuration switch 18.sub.1, sense circuit 14.sub.1 outputs a control signal to switching circuitry 16.sub.1 to switch electrical device 10.sub.1 to an operational mode. In this configuration, electrical device 10.sub.1 will be in operational mode when power switch 17.sub.1 is turned ON. Electrical device 10.sub.3, as shown in FIG. 1, is also configured in a local mode.
An electrical device is configured to operate in a remote mode, as shown by electrical device 10.sub.2, by setting configuration switch 18.sub.2 to a "remote" setting. This enables sense circuit 14.sub.2 to sense a voltage on lines L.sub.1 and L.sub.2. In particular, when electrical device 10.sub.2 is configured in a remote control mode and actuation switch 15 is actuated, an electrical connection is made across lines L.sub.1 and L.sub.2 by contact 13. Sensing circuit 14.sub.2 senses this connection and outputs a control signal to switching circuitry 16.sub.2 to switch electrical device 10.sub.2 to an operational mode. When actuation switch 15 is not actuated, sensing circuit 14.sub.2 does not output the control signal to switch 16.sub.2 and the electrical device is in a standby mode. Hence, in a remote mode, the operational state of an electrical device is dependent on the activation and deactivation of the remotely located actuation switch 15.
When configuration switch 18.sub.1, 18.sub.2 or 18.sub.3 is an "OFF" position, sensing circuit 14.sub.1, 14.sub.2 or 14.sub.3 does not output the control signal to switching circuitry 16.sub.1, 16.sub.2 or 16.sub.3, respectively. Thus, even if power switch 17.sub.1, 17.sub.2 or 17.sub.3 is turned ON, the corresponding electrical device 10.sub.1, 10.sub.2 or 10.sub.3 will not achieve an operational mode.
The conventional configuration, shown for example in FIG. 1, has a number of disadvantages. In particular, each electrical device must be separately configured using external configuration switches 18.sub.1, 18.sub.2 and 18.sub.3. This is inconvenient and inefficient.
Further, installation of a separate actuation switch 15 is necessary to render the electrical devices, configured in a remote control mode to an operational mode. This increases the costs of the system.
Furthermore, in this conventional configuration, when an electrical device configured in a remote control mode is disconnected from the other electrical devices in a series of electrical devices by disconnecting cable 11, that electrical device, and all those connected to it in the series, are turned OFF by sensing circuit 14.sub.1, 14.sub.2 or 14.sub.3. This is particularly disadvantageous if one of the electrical devices is inadvertently disconnected or requires service.